Woodwool (which also means "flakes" and alike) for packaging purposes and as base material for, among others, insulating cement-bonded building boards is mainly sliced using carriage planing machines. Because for the production of woodwool generally waste material of sawing mills and second rated logs are used, of which the growing fibres (the grain of the wood) mostly are not straight and because the wood often contains a lot of knots, in practice preferably only one planing knife is used. In this case the wood is clamped manually in a somewhat inclined position above the carriage of the carriage planing machine, such that during the cutting stroke the planing knife averagely cuts more "into" than "out of" the growing fibres.
For determining the width of the woodwool several measures can be taken. It is possible, that ahead of the planing knife a series of sharpenable or exchangeable width knives (so-called spurs) are mounted. Sharpenable width knives however have the disadvantage that after use they have to be collected, sorted out, sharpened individually, bundled and positioned again very carefully in the planing machine. This is labour intensive and an accurate setting is difficult. Therefore there are also solutions, according to which sets of pre-machined bundled not-sharpenable small and thin width knives are applied for one-time use. However a disadvantage thereof are the cost, whereas these small width knives are easily damaged or broken. For replacement the production of woodwool then has to be interrupted. Further the setting relative to the planing knife and relative to the wood block to be processed causes problems. Width knives extending too far above the planing knife produce a lot of dust in the woodwool, because they do not always precisely follow the same path in carriage planing machines during the forward and during the backward stroke, and because they do not cut grooves at exactly the same position as width knives mounted ahead of the successive planing knife in rotating planing machines. This disadvantage is increased by transversal movements of the wood and/or the carriage.
All types of width knives have the disadvantage that while planing narrow woodwool the space between the width knives becomes that small that woodwool fibres get entangled and the interspaces between the knives get jammed up. As a result the slicing operation has to be stopped in order to be able to clean the width knives. This phenomenon renders it impossible to slice narrow woodwool using width knives, as is desired for packaging purposes or for aesthetically high quality cement-bonded ceiling panels.
In view of the above one has searched for other possibilities for determining the width of the woodwool fibres. These possibilities are provided in the form of so-called comb or profiled knives, as illustrated in U.S. Pat. No. 2,576,190. However, it is a disadvantage of these profiled knives that they cannot or hardly be used for second choice wood, showing cracks, knots and irregularly extending growing fibres. The projecting high wood ribs formed by planing already break before the following cutting edges can slice a second series of woodwool strands at that location. The strips being cut by the tooth points of these profiled knives often follow in an uncontrolled way the irregularly extending growing fibres, such that large pieces break loose from the wood block. Further splinters and, in the case of narrow woodwool, the fibres are clamped into the deep grooves of the profiled knives, whereas sometimes the high small teeth of the profiled knives can break off on hard knots in the wood.
An other alternative is shown by European patent application 19,614, according to which a profiled knife and a flat knife are positioned behind each other. In this case for example a profiled knife with alternating 4 mm wide teeth and 4 mm wide recesses and a following flat knife are used for slicing 4 mm wide woodwool fibres, for example. Using this combination the slicing operation occurs with both knives using the point of the knife and the profiled knife is positioned slightly higher than the smooth knife, such that by means of the profiled knife strands of woodwool are sliced creating grooves in the wood block. These grooves are somewhat deeper than the desired thickness of the woodwool. Next using the flat knife subsequent woodwool fibres having the desired thickness are sliced from the ripples shaped thus. Meanwhile the grooves planed into the wood block by means of the profiled knife still partially remain.
Positioning a profiled knife and a smooth knife behind each other in correspondence with this publication offers the advantage, that the wood can be clamped in a slightly sloping manner, such that both knives in average cut "into" the growing fibre, but an important disadvantage is that with second choice wood, comprising knots and irregular fibre directions, it cannot be avoided that both knives slice irregularly thick fibres and often even splice off slices from the wood block instead of separate woodwool fibres with constant thickness and width. Such undesired phenomenons occur more often when the woodwool fibres to be produced have to be narrow, and slicing regularly shaped very fine woodwool is not possible at all.
Generally it may be noted, that an important disadvantage of the use of profiled knives is, that the side edges of the produced woodwool is ripped out of the grooves by means of the profiled knife instead of cut out. As a result at these side edges of the woodwool fibres frills and hairs are formed, which moreover disengage easily and create a lot of wood dust. Therefore the woodwool fibres, which are subsequently sliced during a successive step (for example by means of a smooth knife) from the remaining ripples neither comprise smoothly cut side edges.
As noted before the width of the woodwool varies because it is dependent upon the presence of, for example, dryness cracks, knots and the path of the growing fibres of the wood at the location of the tooth points of the profiled knives. Therefore the width of the fibres cannot be controlled and is not constant.
The problems mentioned before will increase in magnitude when the quality of the wood is less and the woodwool to be produced has to be narrow, such as if it has to be used for packaging purposes or in decorative ceiling panels, where slices, splinters, hairs and dust are unacceptable.
From the foregoing it has to be concluded that none of the techniques available at the present renders it possible to produce optimally shaped, regular woodwool.
It is an object of the invention to provide a solution.